Currently wireless local communication networks are finding more and more extensive use in the field of information science and videographic communication for the purpose of transmission and distribution of data/information among multiple users located inside the same building (for example, among personal computers, laptop computers, printers and other users located in the same building without any restrictions on the “mobility” of these devices). Transmission of information with the use of WLAN allows one to reduce cost because there is no necessity of laying connecting wires. A network of this type could be also used in those cases when it is either difficult or impossible to lay connecting wires and in cases when there are no socket connectors for local area networks due to architectural restrictions. WLAN represents an ideal solution for a facility at which the arrangement of users is often changed. In existing WLANs, radio communication is usually arranged in compliance with known international standards—for example, such as IEEE 802.11b.
A number of known methods for radio communication in WLAN are based on the use of omnidirectional antennas for signal transmission/reception (See U.S. Pat. Nos. 6,026,303; 6,028,853; 6,192,230). These methods and appropriate equipment enable one to arrange temporary (ad hoc) networks intended for the simultaneous transmission of information to an arbitrary number of users (including users that change their location).
For instance, the method of operation of a wireless data exchange system between multiple wireless stations described in (See U.S. Patent No. 6,192,230) includes the broadcasting of one of the stations (that will transmit data), broadcasting of synchronizing messages and identification of those stations (among a set of stations) for which said data were transmitted. Said method also includes switching of stations selected in the course of broadcasting of said synchronizing messages into an operation mode characterized by relatively high level of power, switching of other stations (i.e. stations for which said data were not intended) into standby mode characterized by relatively low level of power, broadcasting of all data to selected stations and switching the former into standby mode characterized by relatively low level of power following the reception of said data.
The known method allows one to save resources of self-contained power supply sources of network users. At the same time the employment of the omnidirectional radiation of signals imposes a limitation on the network range determined predominantly by the radiation power of a transceiving device and sensitivity of its receiver, which parameters as a rule cannot be significantly improved for WLAN users. In addition, the known method doesn't ensure sufficient reliability of radio communication due to the possibility of emergence of multipath interference in the signal reception point and due to the signal fading effect.
Another transceiving device is known in the art, which is intended for use by WLAN users. This transceiving device comprises a transceiver equipped with an omnidirectional antenna (with said transceiver being connected to a bus, to which a processor, memory and standby mode timer, which in their turn are connected to a self-contained power supply source) connected to transceiver via a switch connected to said standby mode timer and power control circuit (See U.S. Pat. No. 6,192,230).
The known transceiving device increases the service life of a self-contained power supply source of network users. At the same time employment of an omnidirectional antenna in the device limits the network range determined predominantly by the radiation power of a transceiving device and sensitivity of its receiver, which parameters as a rule cannot be significantly improved for mobile WLAN users that are powered from a self-contained source. In addition, the known device doesn't ensure sufficient reliability of radio communication due to the possibility of emergence of multipath interference in the signal reception point and due to the signal fading effect.
Different variants of diversity antenna method and transceivers (that serve as a practical implementation of this method) are widely used to upgrade the reliability of radio communication in WLAN. With this method information is received by an antenna that provides the best quality of a signal being received (See U.S. Pat. Nos. 5,546,397; 5,828,658; 5,748,676).
For instance, U.S. Pat. No. 5,748,676 presents a method for radio communication intended for use in communication networks, in which a receiver has the multitude of antennas. Selection of antenna providing the best conditions of signal reception is performed in the course of reception of a preamble of a data package being transmitted. While enabling one to minimize the influence of signal fading the known method still has the same limitations on the network range that are inherent to methods employing omnidirectional radiation for the purpose of information transmission/reception.
Another transceiving device to be used in WLAN is known (See U.S. Pat. No. 5,748,676). This transceiving device comprises a multitude of antennas connected to a switch by means of which an antenna characterized by the best performance characteristics is switched for radio communication in the course of transmission of data package preamble.
While enabling one to minimize the influence of signal fading the known transceiving device still has the same limitations on the reach range or range of action that are inherent to methods employing omnidirectional radiation for the purpose of information transmission/reception.
In terms of the entire set of essential features, the method for radio communication in a wireless local area network including the transmission (by means of an omnidirectional antenna) of a calibration signal by one transceiving device to another transceiving device that receives this signal also by means of an omnidirectional antenna, identification of the antenna that ensures the best conditions for signal reception among the multitude of omnidirectional antennas of the second transceiving device, transmission of a calibration signal by the second transceiving device via the selected antenna (this calibration signal serves to select the best directional antenna of the first transceiving device in terms of the quality of signal reception), and subsequent radio communication by means of directional antennas of the first and second transceiving devices (those directional antennas that were selected in the course of transmission of said calibration signals) represents the closest analog to the invention being claimed herein (See EPO Application Serial No. 99112131). This is referred to as the reference method.
The use of directed radiation from transceiving devices in the known reference method ensures sufficient reliability of radio communication due to the lowered influence of multipath interference and signal fading. At the same time setting up radio communication at the first stage through the use of an omnidirectional radiation pattern doesn't allow one to increase the range of WLAN users as compared to methods employing diversity antennas. Besides, the use of the known reference method implies that prior to broadcasting a data package it is necessary to transmit a calibration signal twice, which prolongs radio communication session. When it is required to transmit a data package to several users the duration of data package transmission increases in proportion to the number of these users.
The known reference method is implemented by means of transceiving devices (See EPO Application Serial No. 99112131), each of which comprise at least one directional antenna and one omnidirectional antenna with both said antennas being connected via an antenna switchover unit to a movable contact of the reception/transmission mode switch, the fixed contacts of which are connected respectively to receiver input port and transmitter output port. The first output port of the receiver is connected to the first input port of the controller, the second output port of the receiver is connected to the input port of the signal quality measurement unit, the output port of which is connected to the second input port of the controller. The first output port of the controller is connected to the antenna switching unit, the second output port of the controller is connected to the first input port of the transmitter, and the third output port of the controller is connected to the second input port of the transmitter. The controller is capable of two-way communication with a memory unit and user interface.
The known reference transceiving device allows one to enhance the reliability (quality) of radio communication between two users due to the reduction in the multipath interference and signal fading. However, these advantages are attained at a sacrifice of increase in transmission time of each data package and absence of a possibility of simultaneous transmission of data to several users in a network. The known reference transceiving device doesn't enable one to increase the range of WLAN as compared to methods employing diversity antennas because at the first stage of communication both transmission and reception are carried out by means of omnidirectional antennas.